Open AccessОсобенности фазообразования TbBO-=SUB=-3-=/SUB=- при изотермических отжигах
Author(s) -
И.М. Шмытько
Publication year - 2019
Publication title -
fizika tverdogo tela
Language(s) - English
Resource type - Journals
eISSN - 1726-7498
pISSN - 0367-3294
DOI - 10.21883/ftt.2019.02.47136.228
Subject(s) - annealing (glass) , vaterite , triclinic crystal system , microcrystalline , materials science , amorphous solid , monoclinic crystal system , crystallization , crystallography , terbium , mineralogy , analytical chemistry (journal) , chemical engineering , chemistry , crystal structure , metallurgy , composite material , organic chemistry , calcium carbonate , optoelectronics , luminescence , engineering , aragonite
Detailed X-ray studies of changes in the structure of terbium orthoborate TbBO_3 in the course of successive high-temperature isothermal annealing of the initial mixture in the form of an amorphous precursor and in the form of a homogenized mixture of microcrystalline Tb_7O_12 and B_2O_3 powders have been carried out. It is shown that the formation of TbBO_3 crystals in both cases occurs through the formation of intermediate two-phase states. Particularly, the triclinic high-temperature ν-TbBO_3 phase is formed already at the first crystallization stages (about 600°C) almost simultaneously with the equilibrium vaterite modification of TbBO_3 (sp. gr. P 63/ mmc ) during low-temperature annealing of an amorphous precursor, which transforms into the vaterite modification at an annealing temperature of 850°C. The phase of monoclinic terbium trioxoborate TbB_3O_6 is formed at the first stages of phase formation (about 800°C) almost simultaneously with the vaterite phase when the feedstock is annealed in the form of a homogenized mixture of microcrystalline Tb_7O_12 and B_2O_3 powders. It also transforms into the vaterite modification at an annealing temperature of 950°, which is preserved up to the highest annealing temperatures in the experiment (1200°C). A hypothetical explanation of the formation of such two-phase states during low-temperature annealing of the feedstock and their disappearance at higher annealing temperatures is proposed.